There exists in the foam product industry a wide variety of methods and apparatus for forming foam slabstock products. Presently, the industry places heavy reliance on flat-top equipment systems and conversion kits. These flat-top equipment systems and conversion kits typically involve the general concept of applying rising foam to a fixed main trough with an open top and confining side walls. The main troughs often feature an initially sloped underlying support structure which abuts a downstream moving horizontal support surface such as a horizontal conveyor.
In these systems, sheets or films of paper or plastic are positioned between the rising foam and the bottom supporting surface and the side walls. The sheets (or films-the two words being used interchangeably herein) travel together with the foam material in the main trough to reduce frictional contact between the respective surfaces and to facilitate travel of the foam material within the main trough. The film material on the sides comes in contact with the interior surface of a side wall or a conveyor as the film material extends from a foam material introduction point until removal at a point downstream of the foam slabstock's full rise position. The films used in these systems typically have a bottom edge that extends horizontally and is aligned with the lower edge of the side walls.
Foaming material introduced into the main trough, however, expands vertically up and down while travelling downstream. The use of side films having horizontally extending upper and lower edges does not account for this vertical rise component in the foam, and therefor friction develops between the side film and the vertically rising foam. The shearing or rubbing of the rising foam material against the horizontally extending side sheets leads to the production of foam slabs with elongated rounded corners and a generally dome shaped upper surface.
The prior art includes a plurality of systems which have been designed in an effort to reduce this vertical rise friction so as to decrease the length of the rounded corners and to increase the height of the vertical sides. Reference is made to U.S. Pat. Nos. 3,091,811; 3,719,734; 3,751,197; 3,809,512; 3,812,227, 3,875,276 and 4,559,003 which are directed at foam slabstock production systems which, in addition to the usual main side films, incorporate additional secondary side films that are used in conjunction with the main side films. The secondary side films are either lifted up or drawn at an upward angle in an effort to lessen the friction on the vertically rising foam. These systems, which rely on secondary film systems, suffer from a variety of drawbacks such as friction development between the secondary and main films, a typically much more complex and difficult system to run, an increased chance for wrinkling to occur in the films, a tendency for side splits to develop and a high amount of waste film production.
Prior art systems also utilize fall plates as the underlying support surface. These fall plates have a downward slope that can be adjusted. In an effort to avoid rounded bun corners, attempts have been made to "hang" the foam on the side plastic by choosing steep inclines for the fall plates. However, these fall plate adjustments can lead to foam processing problems such as side splits.
U.S. Pat. No. 4,605,683 discloses a foam slabstock production system which features a protective film that is wrapped around an inclined conveyor system and then redirected near the downstream end of the conveyor system along the further downstream extending sidewalls of the main trough. The moving conveyor extends at an upward incline from a point near the foam introduction location and terminates near the foam's full rise position. The introduced foam material floats over a supporting liquid of higher specific gravity held in a tank while in an expanding state. The conveying means is preferably submerged in the supporting liquid, and a release agent and a solvent are added to the liquid in the tank to inhibit adherence of the polymer to the conveyor and the submerged protective film wrapped about the conveyor. This prior art system introduces the added complexity of having a conveyor running in an area where the foam material is highly turbulent and still in a highly fluid or liquid state. The system of U.S. Pat. No. 4,605,683 further requires the introduction of solvents and release agents to prevent adherence of foam to the submerged components and thus introduces added costs and further safety and waste disposal concerns. In addition, this prior system places moving parts in contact with the film which can make wrinkling control difficult.